KTU Open Journal Systems (Kaunas University of technology)
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Effect of Chemical Composition and Isothermal Treatment Duration on Nano-bainite Steels
No full textEffect of chemical composition and isothermal treatment duration on nano-bainite steels is investigated in this work. The steels that contain Co, V and Al elements with high C are designed and produced. The nano-bainite microstructures can be obtained by the isothermal treatment in the Co and Al co-alloyed sample. Its mechanical properties and wear resistance performance are tested. Its microstructures were detected using a FESEM. After the steel is austensitized at 950 ℃ for 30 minutes and is subsequently isothermally-treated at 260 ℃ for 2 hours, the nano-bainite structures can be obtained, whose microstructures also contain martenite and residual austenite in addition to nano-bainite. The isothermal time of 120 minutes is enough to obtain sufficient nano-bainite, which forms due to the addition of both Al and Co, which accelerate the austenite → bainite transformation, since Al and Co increase the free-energy difference between ferrite and austensite and the reaction rate for obtaining nano-bainites. The fracture toughness of the nano-bainite steel obtained by the isothermal transition is obviously better than the quenching + tempering steel for the Co and Al co-alloyed sample. The fracture morphology of the Charpy impact test shows that the fracture is ductile. Although nano-bainite steel has the poor wear-resistance performance the initial stage compared to quenching + tempering steel, it shows more and more wear resistance performance with increasing wear time
Mechanical and Durable Performance of Lime-Steel Slag-Coal Gangue Mixtures Prepared by a Uniform Design Method for Pavement Base Applications
No full textTo reduce the accumulation of coal gangue and steel slag, a mixture of lime-steel slag-coal gangue for pavement base was prepared. Six groups of lime-steel slag-coal gangue mixtures were designed using a uniform design method. The 7 d unconfined compressive strength, 180 d compressive resilience modulus and 180 d splitting tensile strength tests, the freeze-thaw cycles, and the wet and dry cycles were carried out to study the mechanical properties, frost resistance and water stability. The expansion effect of f-CaO in steel slag on the mixtures was investigated by water immersion. SEM was used to explore microscopic changes in the mixtures. The field application of coal gangue mixture was carried out for two years. The results show that the regression equations obtained by the uniform test have high accuracy. With the increase of lime in the mixture, the mechanical strength, frost resistance, and water stability of the mixtures were first enhanced and then decreased. With the increase of steel slag, the unconfined compressive strength increased, the compressive resilience modulus increased at first and then decreased, the splitting tensile strength decreased, the BDR value decreased, and the strength loss of water stability increased gradually. The internal structure of the mixtures is stable and has good frost resistance. There is no obvious microscopical difference before and after freeze-thaw cycles. The immersion expansion rate of the mixtures was far less than 1.5 %
Comparison of Mathematical Surface Energy Models and Fuzzy Approach Pertaining to Surface Energy Level of Polylactic Acid and Linear Low-density Polyethylene
No full textThe usage of flexible film in the food packaging industries has been rapidly increasing over the past few years. In flexible printing process, the wettability and adhesion of polymer substrates depend on the surface composition, roughness, energy level and tension. Among all these properties, the Surface Energy Level (SEL) of polar and nonpolar polymer substrates were determined by measuring Contact Angle Values (CAV). This study focuses on experimentation based SEL measurement using corona treatment for both treated and untreated LLDPE (Linear Low-Density Poly Ethylene) and PLA (Polylactic Acid) films using MSEM (Mathematical Surface Energy Models) such as Fowkes, Owens-Wendt, and Wu based on the CAV of polymer films and further to develop a Mamdani fuzzy interface based model for predicting optimum SEL with help of experimentally generated data. The observed SEL of untreated and treated PLA and LLDPE films were 40 and 38, 48 and 44 mN/m respectively. Fuzzy-based simulations showed similar results, with treated PLA and LLDPE at 45.4 and 44. Finally, the proposed Mamdani model can predict SEL with high accuracy in comparison with experimental results and the good printability of ink adhesion was achieved in treated than the untreated films.
Effect of Reaction Temperature on the Synthesis of TiO2 from Titanium Slag and Sodium Hydroxide via Heat Treatment
No full textTitanium dioxide (TiO2) is important in many industrial fields. Industrial TiO2 is mainly produced from ilmenite and rutile ore, two abundant global resources. Studies have shown that the calcination method with NaOH can help prepare TiO2 from titanium slag. In this study, the effect of reaction temperature between titanium slag and sodium hydroxide (NaOH) was investigated in the process of separating TiO2 from titanium slag. The formed product was evaluated for TiO2 content, Fourier Transform Infrared Spectroscopy, X-ray diffraction, and Scanning Electron Microscopy to evaluate the properties. The results showed that the reaction temperature had a significant effect on the TiO2 content of the product after separation. The TiO2 content decreased with increasing reaction temperature. The decrease in content is due to increased hydroxyl groups in the product. At a reaction temperature of 700 °C, the product had the highest TiO2 content of 96.78 wt.%. The results also indicated that the product\u27s main allotropic form of TiO2 is rutile
Performance Analysis of Concrete Materials for Dam Body Energy Storage Modified by Graphene Oxide
No full textThis study primarily focuses on the modification of concrete materials by incorporating graphene oxide (GO). The dispersion of GO in concrete was characterized through Fourier transform infrared spectrometer (FTIR) and scanning electron microscopy (SEM), and the ability of concrete specimens with varying GO content to endure mechanical and climate temperature challenges were investigated. Additionally, the energy conversion relationship during uniaxial compressive failure was analyzed. The experimental results show that when the GO content is 0.05 %, the top stress, top strain, ultimate strain, and elasticity modulus increase by 29.54 %, 23.41 %, 61.72 %, and 34.93 %, respectively, relative to the reference concrete. With a GO content of 0.03 %, the GO/recycled cement-based composite material exhibits the greatest strength improvement after 7 days of hydration. At a 0.02 % GO content, the GO/recycled cement-based composite material exhibits the most notable strength enhancement after 28 days of hydration. Relative to conventional concrete, GO substantially boosts the key characteristics of uniaxial compression tests, notably diminishing the rate at which elastic strain energy is discharged, increasing the dissipation energy, decreasing the brittleness, and augmenting the malleability and toughness of concrete. However, efficient dispersion and cost-effective production methods for GO have not yet been achieved, and there are no long-term engineering applications of GO-modified concrete. Further research into GO-modified concrete technologies is recommended to promote the practical application and production of GO-incorporated concrete composites
Uniaxial Compression Performance of Recycled Brick Aggregate Concrete with Basalt Fibers and its Bonding Performance with Steel Bars
No full textThis paper systematically analyzes the basic mechanical properties, uniaxial compression performance, and bonding performance of recycled brick aggregate concrete treated with basalt fibers with steel bars. The results show that the addition of recycled brick aggregate not only reduces the basic mechanical properties and uniaxial compression performance of recycled brick aggregate concrete but also reduces the bonding performance between concrete and steel bars. The addition of basalt fiber can increase the cube compressive strength and splitting tensile strength of recycled brick aggregate concrete by 18.66 % and 22.68 %, respectively, and increase the uniaxial compressive stress and strain by 20.59 % and 11.11 %, respectively. Basalt fiber can effectively improve the bonding performance between recycled brick aggregate concrete and steel bars, increasing the peak bonding strength by 1.17 MPa and reducing the peak slip by 0.136 mm. A calculation model for the uniaxial compressive stress of basalt fiber recycled brick aggregate concrete and a calculation model for the bond strength between basalt fiber recycled brick aggregate concrete and steel bars were constructed
Water Quality Simulation of Reclaimed Water Supply Type Rivers and Application of Metal Organic Frameworks in Phosphorus Pollution Control
No full textThis study focuses on the Xinfeng River, a regenerated water supply type river, and conducts water quality simulation and research on the application of metal organic framework materials (MOFs) in phosphorus pollution control. Using the storm water management model (SWMM) and environmental fluid dynamics code (EFDC) coupling model, the water quality changes of Xinfeng River under different scenarios of reclaimed water supply were simulated. The model was calibrated and verified through historical monitoring data, and the results showed that chemical oxygen demand (COD) could stably meet the Class V water quality standard, while NH3-N and total phosphorus (TP) could not meet the standard. Secondly, NH2-MIL-125(Ti) and NH2-UIO-66(Zr) were synthesized in this study. The morphology, structure, and properties of MOFs were characterized using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), and thermogravimetric analysis (TGA), and they were used for adsorption and removal of phosphorus in water environments. The results indicate that NH2-MIL-125(Ti) has a larger adsorption capacity (10.42 mg/g), and the adsorption of phosphorus by NH2-MIL-125(Ti) and NH2-UIO-66(Zr) is more in line with the quasi second order kinetic model, and their adsorption isotherms are more in line with the Freundlich model. In addition, both adsorbents have good adsorption regeneration performance, with a phosphorus removal rate of over 85 % after 5 cycles. The water quality simulation model constructed in this study can accurately predict the impact of recycled water supply on river water quality. The selected MOFs materials have good phosphorus adsorption and removal performance, providing a scientific basis and technical support for improving water quality and controlling phosphorus pollution in recycled water supply rivers
Residual Mechanical Properties of Fire-Damaged Concrete: NDT/DT Evaluation
No full textEvaluating the residual mechanical properties of fire-damaged concrete is crucial for structural safety, yet the limitations of destructive testing (DT) have promoted the use of non-destructive tests (NDT), for effective in-situ assessment. This research explores the residual mechanical behavior of concrete and examines the predictive accuracy of NDT/DT in post-fire conditions. Concrete cylinders with consistent mix designs were subjected to temperatures ranging from 200 °C to 1000 °C, following a controlled natural fire curve applied via an electric furnace. After maintaining the target temperature for 90 minutes and allowing for natural cooling, DTs (compressive strength and stress-strength behavior) and NDTs (UPV and rebound hammer tests) were carried out. The static and dynamic elastic moduli were not directly tested but were derived using empirical correlations with UPV values. Temperature evolution inside the specimens was simulated using SAFIR software. The findings demonstrated a marked deterioration in mechanical performance beyond 400 °C, with compressive strength losses exceeding 80 % at 800 °C, both static and dynamic elastic moduli were reduced by nearly 98 %. Post-fire stress-strain behavior also indicated substantial losses in stiffness and ductility beyond 600 °C. UPV measurements correlated strongly with the decrease in residual strength. A regression model was developed to estimate residual compressive strength based on UPV results, validating the technique’s relevance for post-fire assessments. The combined application of DT and NDT methods yielded a detailed understanding of thermal degradation. Notably, UPV demonstrated high sensitivity in detecting internal damage and estimating residual stiffness in fire damaged concrete. It thus offers engineers a reliable tool for evaluating whether repair or replacement is necessary, especially in contexts where DTs are not feasible
Kalbų konkurencijos atspindžiai Dieveniškių apylinkių kalbiniame kraštovaizdyje XX a. pr. – XXI a. pr.: antkapinių užrašų kiekybinis tyrimas
No full textXIX a. pab. – XX a. pr. vykusi intensyvi etnolingvistinė Pietryčių Lietuvos gyventojų kaita labiausiai paveikė rytinius lietuvių kalbos arealo paribius. Pasak kai kurių autorių, praradusios kontinuumą su pagrindiniu lietuvių kalbos masyvu, galutinai išnyko dauguma lietuvių kalbinių salų (Gaučas, 1993; Zinkevičius, 2008). Remiantis XIX a. pab. – XX a. pr. šaltiniais (Anonim, 1898; Rozwadowski, 1901) ir 2021 m. gyventojų surašymo duomenimis, per 130 metų lietuviškai kalbančiųjų skaičius paskutinėje iš salų – Dieveniškių krašte – sumažėjo daugiau nei 13 kartų (nuo 7 108 iki 512), ir apie 2021 m. lietuviakalbiai tesudarė tik 24 proc. vietos gyventojų.
Kiekybinis Dieveniškių antkapių užrašų (iš viso ištirta 4 367 antkapinių užrašų) tyrimas leido statistiškai įvertinti per pastarąjį šimtmetį vykusią lietuvių ir slavų kalbų sąveiką ir parodyti jos įtaką kalbinei kaitai.
Išanalizuoti duomenys rodo, kad tiriamoje vietovėje dominuoja užrašai lenkų kalba, kurie sudaro 69 proc. visų užrašų. Tačiau užrašų lietuvių kalba nuolat daugėjo: nuo mažiau nei 13 proc. iki 1940 m. iki daugiau nei 37 proc. per pastarąjį dešimtmetį.
Tyrimo rezultatai atskleidžia, kad Dieveniškių apylinkėse rašytinės lietuvių kalbos prestižas didėja. Šis procesas ypač sustiprėjo po 1990 m., atkūrus Lietuvos valstybę. Kultūrinę ir kalbinę gyventojų kaitą galimai lemia valstybinės kalbos statuso stiprėjimas regione
CLT Wall for Bullet-Safe Temporary Buildings
No full textThe authors propose a handgun bulletproof load-bearing 140 mm cross-laminated timber (CLT) wall with knitted aramid (Kevlar) fabric in two layers for tangling the bullet and a reference wall without a Kevlar layer. The study compares the layers in which the added aramid sheet should be placed for northern areas to allow people to have acceptable insulated conditions in temporary houses while being protected from potential bullet external threats. Results showed that a 140 mm CLT layer with 200 mm mineral wool insulation with a Kevlar layer between the insulation layer and CLT is enough to stop the bullet if fired up to 341.6 m/s with a firearm. Perforation data for CLT material samples with various thicknesses have been collected and analyzed. A metal rod and a ruler determined the penetration depth for ogive-nose projectiles when they did not fully perforate the panel. The results show the ballistic properties of CLT material. The results will be proposed to the construction industry of wooden buildings as a bonus for those whose security is significant